Polyvinyl chloride (PVC) homopolymers and copolymers are the most widely employed polymers in industry and can be used for many products, from thin surgeon's gloves to rigid durable pipe. Various additives can be added to PVC to provide processability and those melt characteristics required for a particular process. For example, stabilizers, plasticizers, processing aids and lubricants are generally added to molding compositions, as well as desired colorants and fillers.
Lubricants are added to PVC to modify the melt viscosity and melt flow properties during processing. The most commonly employed lubricants include waxes, metal soaps of fatty acids and fatty esters. Lubricants that are somewhat soluble in PVC and lower the apparent melt viscosity and reduce internal shear, with its consequent generation of heat, are referred to as internal lubricants. Lubricants that are insoluble in PVC and form a thin layer around the PVC particles, reducing adhesion of the polymer to processing equipment and reducing internal heating, are referred to as external lubricants.
Internal lubricants for PVC must have a low molecular weight, i.e., less than about 7,000, a melting point within the processing temperature range, some solubility in the polymer, and have a nonpolar hydrocarbon chain in the molecule which acts as a lubricant layer.
Since lubricants are generally imcompatible with PVC, any excess lubricant present bleeds out of the resin and collects at the surface of the molded article, causing staining and other side effects. Thus the least amount of lubricant will be employed in a molding composition that can adequately perform the lubricant required.
For the record industry, a particular type of room temperature solid esterified montan wax, such as Wax E of the Hoechst Company, is employed worldwide as the lubricant for compression molding of records and is regarded as the most effective lubricant known to date. It is generally employed in amounts of about 0.4-0.5 percent by weight of the total resin composition. A more effective lubricant would be desirable.